As concerns continue to mount with respect to carbon emissions associated with conventional electric power generation systems, additional funding and research has been undertaken with respect to systems that use renewable energy resources, such as solar power, wind power, geothermal energy, and the like. With more particularity regarding solar cells, such solar cells are designed to convert at least a portion of available light into electrical energy. Solar cells are generally based upon semi-conductor physics, wherein a solar cell comprises a PN junction photodiode with a light sensitive area. The photovoltaic effect, which causes a solar cell to convert light directly into electrical energy, occurs inside a semiconductor material where light knocks off electrons. Because of the structure of the cell, there is an induced field that causes the electrons to flow in one direction and collect at the terminals. The structure of the solar cell is based in a PN junction composed of two layers: a p-type semiconductor and an n-type semiconductor. The interface where the two join is referred to as a junction.
For enhanced performance in GaAs solar cells, two additional layers, which are electrical contact layers, are also present. These contact layers enhance electric current that flows out of and into the solar cell. In conventional designs for solar cells that include compound semiconductors, the electrical contact layers reside on opposing sides of solar cells (a front side and a back side, respectively). The front side of the cell is the side that is configured to be directed towards a light source (the Sun) to receive radiation. Typically, the electrical contact layer on the front side of the cell is formed in a grid-like pattern, which includes a plurality of metallic fingers that are manufactured to be as small as possible so as to limit blockage of light prior to the light reaching the absorber region. The electrical contact layer on the back side of the solar cell generally covers the entire back side of the solar cell.
Manufacturing a solar cell with all backside contacts has been extensively explored, particularly for silicon solar cells. This type of solar cell has the advantage of all metallization residing on the back of the cell, giving the opportunity to independently optimize the front and back of the cell for optical and electrical performance, respectively. Back contacted solar cells are ideal for concentration applications, and researchers have been able to create 27.5% efficient silicon cells under 100 suns. Silicon, however, is an indirect band gap semiconductor, which requires a thick layer of material to absorb the solar spectrum. Currently, manufacture of an efficient all-back side solar cell that includes compound semiconductors has not been achieved.